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Chip Amps Amplifiers based on integrated circuits

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Old 9th July 2003, 09:15 PM   #11
Magnetmaz is offline Magnetmaz  United States
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Thanks for the help.

I'm going to try this again, on my last chip...trying hard to not bend the pins...

and i will put both grounds on a wood board or something so i can be sure they don't interact with the heat sink.

-Maz
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Old 9th July 2003, 09:16 PM   #12
Magnetmaz is offline Magnetmaz  United States
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In regards to your suggestion, Tschrama:

You want me to measure the Voltages from each of the 5 pins to ground?

-Maz

Pin# Voltage
1 32.8
3 0
4 -36
7 0
8 0


the rails, before rectification are 24, 0, -24. After they are somewhere around 36 and -36
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Old 9th July 2003, 10:00 PM   #13
Peter Daniel is offline Peter Daniel  Canada
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If they are the same before rectification (the rails) they should be the same after, on pins 1 and 4, but your measurements show different. It seems like your package is an insulated version (TF) so don't worry about connecting case with a ground
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Old 10th July 2003, 10:25 AM   #14
carlosfm is offline carlosfm  Portugal
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Talking Whait a minute...

On the picture there is an LM3875TF chip.
Isn't this the isolated version?
What's there to isolate, guys?

If there was a short the fuses had blown already.
I think it's just a question of wires connected to the incorrect pins of the chip.
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Old 10th July 2003, 03:13 PM   #15
Magnetmaz is offline Magnetmaz  United States
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I completely rewired up the chip today. Voltages all look good. 36 and -36V from the correct pins to ground.

I even hear a very weak signal coming from the speakers, albeit VERY distorted.


2 questions :


1) Do i have to have an input pot, or resistor to ground? Currently i have my signal hardwired in.

2) My input capacitor is POLAR. I have it wired the correct way, with positive side seeing the input signal.... But could this be my problem? I used all Panasonic FC caps ( all polar ), as suggested by someone on the forum as a cheap alternative to Black Gates.

-Maz
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Old 10th July 2003, 03:25 PM   #16
Peter Daniel is offline Peter Daniel  Canada
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Even without pot, you don't need resistor to ground, just series resistor from input to inverted input pin. The orientation of the cap doesn't make any difference. You don't even need a cap, but be carefull with DC offsets. Before connecting speaker measure it.
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Old 10th July 2003, 06:05 PM   #17
ronc is offline ronc  United States
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Sounds to me like a +/- voltage inbalance. Although all i use is battery power for my GCs i had one battery go low on me and the sound was very very distorted and weak.
ron
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Old 10th July 2003, 07:11 PM   #18
Cradle22 is offline Cradle22  Germany
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Hi!

Try it without the input cap, I've build GCs with LM3875, LM3876, OPA549 and OPA548, never had to use an input cap (but, I have to admit, my source never changes, as well...)

And I do bend the pins of the ICs, so far it seems that nothing has been broken...

And you can also try putting power and signal ground on one star point... for my GCs seperating them never made a difference... I actually do not really use a star, but a long solid core cable without isolation, directyl soldered to the ground pin of the power connector, something like this:

_________ \ / \ | /
GROUND O-----------------------------
_________ / \ / | \

(Darn! That MessageBoard software erases spaces, just like html...)
Don't give up!

Bye,

Arndt
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Old 10th July 2003, 07:18 PM   #19
tschrama is offline tschrama  Netherlands
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I think we can really realy help you if you post all exact DC and AC voltages of ALL pins (use input ground as ref, this should be a starground ) , voltage supply points, exact chip type and the exact circuit you are using. This force you to go over this once more to re-re-re-check everything.
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